Question: If $a + b = 9$ and $x + y = -7$, what is $10y - 5a + 10x - 5b$ ?
Explanation: $= -5a - 5b + 10x + 10y$ $= (-5) \cdot (a + b) + (10) \cdot (x + y)$ $= (-5) \cdot (9) + (10) \cdot (-7)$ $= -45 - 70$ $= -115$